Geologist: A new method for forecasting earthquakes has reliably predi

Question

Geologist: A new method for forecasting earthquakes has reliably predicted several earthquakes. Unfortunately, this method can predict only that an earthquake will fall somewhere within a range of two and a half points on the Richter scale. Thus, since a difference of two and a half points can be the difference between a marginally perceptible shaking and a quake that causes considerable damage, the new method is unlikely to be useful.

Which one of the following, if assumed, enables the geologist's conclusion to be properly inferred?

(A) Even if an earthquake-forecasting method makes predictions within a very narrow range on the Richter scale, this method is not likely to be useful unless its predictions are reliable.

(B) An earthquake-forecasting method is unlikely to be useful unless its predictions always differentiate earthquakes that are barely noticeable from ones that result in substantial destruction.

(C) An earthquake-forecasting method has not been shown to be useful until it has been used to reliably predict a large number of earthquakes.

(D) Several well-established methods for forecasting earthquakes can predict within much narrower ranges than two and a half points on the Richter scale.

(E) An earthquake-forecasting technique, even a perfectly reliable one, will probably be of little use if its predictions never distinguish between earthquakes that are imperceptibly small and those that cause catastrophic damage.

ankushsambare · Answer

Conclusion:
The new earthquake forecasting method is unlikely to be useful.
Why?
 
 The method predicts earthquakes only within a wide range: 2.5 Richter points. 
 A 2.5-point difference could mean either a tiny quake or a damaging one. 
 So the geologist thinks the method is not useful.  
To make this conclusion valid, we need an assumption saying:
If a forecasting method cannot distinguish between harmless and dangerous earthquakes, it is probably not useful.
Check choices:
(A) Talks about reliability. The method is already said to be reliable, so irrelevant.
(B) Too strong because it says predictions must “always” differentiate. The conclusion only says “unlikely to be useful,” not impossible to be useful.
(C) Talks about needing many predictions. Irrelevant.
(D) Comparing with other methods does not prove this one is useless.
(E) Correct. It says even a perfectly reliable method will probably be of little use if it cannot distinguish between tiny earthquakes and catastrophic ones. This directly supports the conclusion.
 Answer: (E)

TheYagami · Answer

correct ans should be E 
It says even a perfectly reliable technique is of little use if it cannot distinguish tiny and catastrophic earthquake

guddo · Answer

Geologist: A new method for forecasting earthquakes has reliably predicted several earthquakes. Unfortunately, this method can predict only that an earthquake will fall somewhere within a range of two and a half points on the Richter scale. Thus, since a difference of two and a half points can be the difference between a marginally perceptible shaking and a quake that causes considerable damage, the new method is unlikely to be useful. 
 
Which one of the following, if assumed, enables the geologist’s conclusion to be properly inferred?

The geologist accepts that the method has made reliable predictions, but says it is unlikely to be useful because its predicted range is too wide.  The missing principle  must connect that wide range to usefulness: a useful earthquake forecast must  always distinguish minor earthquakes from seriously damaging ones .

(A) Even if an earthquake-forecasting method makes predictions within a very narrow range on the Richter scale, this method is not likely to be useful unless its predictions are reliable.

Wrong. This says reliability is necessary, but the method already has reliably predicted several earthquakes. It does not explain why the 2.5-point range makes the method unlikely to be useful.

(B) An earthquake-forecasting method is unlikely to be useful unless its predictions always differentiate earthquakes that are barely noticeable from ones that result in substantial destruction.

Correct. The new method gives only a 2.5-point range, and such a range can fail to distinguish between a barely noticeable earthquake and a damaging one. If a method is unlikely to be useful unless it always makes that distinction, then the geologist’s conclusion follows.

(C) An earthquake-forecasting method has not been shown to be useful until it has been used to reliably predict a large number of earthquakes.

Wrong. The issue is not the number of predictions. The geologist’s reasoning is based on the width of the predicted Richter-scale range.

(D) Several well-established methods for forecasting earthquakes can predict within much narrower ranges than two and a half points on the Richter scale.

Wrong. Other methods may be better, but that does not prove this new method is unlikely to be useful.

(E) An earthquake-forecasting technique, even a perfectly reliable one, will probably be of little use if its predictions never distinguish between earthquakes that are imperceptibly small and those that cause catastrophic damage.

Wrong. This is too extreme. The stimulus says the method can fail to distinguish between minor and damaging earthquakes, not that it never makes such distinctions.

Answer: (B)

BongBideshini · Answer

Why is E wrong, as per my understanding
The range of the Imperceptible Shake and Catastrophic Damage will be way more than 2.5
Example:
 
 Imperceptible Shake: 2.0 
 Catastrophic Damage: 7.0  
Our new method makes a prediction and gives us a 2.5-point window.
So, for example, if the method predicts an upcoming quake in the 1.0 and 3.5 range, we know that the Catastrophic Damage will not happen 
And if the method predicts an upcoming quake in the 6.0-8.5 range, it means there is no Imperceptible Shake.
So, this new method is useful to segregate the two extreme cases; the condition " if its predictions never distinguish between earthquakes that are imperceptibly small and those that cause catastrophic damage " never arises.

egmat · Answer

Hi BongBideshini,

Your instinct is pointing the right way (E really is wrong), but let me sharpen  why , because the decisive issue isn't the size of the real-world gap. It's a single quantity word:  "never."

Look at what the argument actually tells us about the method. It says a  2.5 -point range  "can be" the difference  between a barely perceptible shake and a damaging quake. "Can be" means the method  sometimes  fails to distinguish minor from damaging - not that it always fails, and not that it never distinguishes. As you noted, in some windows it clearly does separate the extremes.

Now read E's condition: "if its predictions  never  distinguish..." For an assumption to  enable  the conclusion, its "if" part has to actually describe the geologist's method. But this method doesn't "never distinguish" - it distinguishes sometimes. So E's condition simply isn't met, and an assumption whose trigger never fires can't push us to "unlikely to be useful." That's the flaw:  too strong / wrong quantifier , not the magnitude argument you built.

Compare  B , which uses " always  differentiate." B says: to be useful, a method must  always  separate barely-noticeable from destructive quakes. The geologist's method fails to  always  do this (that's exactly what "can be the difference" establishes) - so it's unlikely useful. The link closes cleanly.

Turn the one knob to feel it:

- "...useful unless it  always  distinguishes" - method fails sometimes -  conclusion follows  (this is B).
- "...little use if it  never  distinguishes" - method  does  distinguish sometimes -  condition never triggers  - no help (this is E).

So the winner hinges on matching the method's  sometimes-fails  behavior to " always ," not " never ."

Answer: B

kumarvibhuti630 · Answer

Premise 1: A new method for forecasting earthquakes has reliably predicted several earthquakes.
Premise 2: Unfortunately, this method can predict only that an earthquake will fall somewhere within a range of two and a half points on the Richter scale.

Conclusion: since a difference of two and a half points can be the difference between a marginally perceptible shaking and a quake that causes considerable damage, the new method is unlikely to be useful.

Gap Between Premise and conclusion:  
 1. Able to identify between marginal and considerable is mostly required for usefulness 
 2. Only able to identify large or small is not useful

(A) We are not talking about reliability

(B) Correct , as it correctly defines the gap.

(C) Irrelevant, out of scope

(D) This though support the conclusion, is not must required for the conclusion to hold true

(E) we are not concerned about small or very big earthquakes( catastrophic)- as suggested in Gap 2.

yc168 · Answer

OE for reference:

Overview:  
The geologist talks about a new method for forecasting earthquakes that has reliably predicted several earthquakes. The premises of the geologist's argument are that the method can predict only that an earthquake will fall within a range of 2.5 points on the Richter scale and that 2.5 points can be the difference between a marginally perceptible shaking and a quake that causes considerable damage. The geologist concludes that the new method is unlikely to be useful.
You are asked to identify an assumption that will enable this conclusion to be properly drawn from the premises. Notice that it follows from the two premises that the new method cannot pin down the severity of a quake well at all: its prediction for the severity of a given quake might range from being just marginally perceptible shaking to causing considerable damage.

The Correct Answer:

B  (B) lays out a standard for identifying earthquake prediction methods that are unlikely to be useful. If the method does not always differentiate quakes that are barely noticeable from ones that cause substantial destruction, it is unlikely to be useful. As noted in the "Overview," it follows from the premises of the argument that when the new forecasting method predicts a quake, the forecast for its severity might range from being just marginally perceptible to causing considerable damage. Since there's no real difference in meaning between "barely noticeable" and "marginally perceptible," or between "considerable damage" and "substantial destruction," the new method is unlikely to be useful according to the standard in (B). Thus the conclusion of the argument follows logically once (B) is assumed.

The Incorrect Answer Choices:

A  (A) lays out a standard for identifying earthquake prediction methods that are unlikely to be useful, but the crucial part of that standard is reliability: a method is not likely to be useful unless its predictions are reliable. There is some indication that the new method is a reliable predictor in that it is said to have reliably predicted several earthquakes. On the other hand, there is no basis for considering the new method to be unreliable, and if the new method is not shown to be unreliable, then the standard in (A) does not allow us to conclude that the method is unlikely to be useful.

C  The conclusion of the argument is that the new method is unlikely to be useful. (C) says that a method won't be shown to be useful until it has a long and reliable track record. But (C) gives us no reason to think that the new method won't one day have a long and reliable track record. So assuming (C) does not establish that the new method is unlikely to be useful.

D  (D) says there are well-established methods that can predict earthquakes within narrower ranges than 2.5 points on the Richter scale. But it's possible that the new method is more reliable than these well-established methods, or that it has some other advantage. So assuming (D) does not establish that the new method is unlikely to be useful.

E  (E) lays out a standard for identifying earthquake prediction methods that are unlikely to be useful. Even if a method is perfectly reliable, if it does not distinguish quakes that are  imperceptibly small  from ones that  cause catastrophic damage , it is unlikely to be useful. As noted in the "Overview," it follows from the premises of the argument that when the new forecasting method predicts a quake, the forecast for its severity might range from being just  marginally perceptible  to  causing considerable damage . But notice that the standard in (E) is not strict enough to allow us to draw the conclusion that the new method is unlikely to be useful. (E) invokes a very wide range of earthquake severity, and the new method, as portrayed by the premises of the argument, is capable of distinguishing some quakes within that range.

Geologist: A new method for forecasting earthquakes has reliably predi

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Geologist: A new method for forecasting earthquakes has reliably predi

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